The purpose of this study is the investigation of physical factors which limit the use of videodensitometry to quantitate physiological parameters from images obtained using Digital Subtraction Angiography (DSA) following intravenous injection of contrast material, and the evaluation of proposed correction methods. Central to that goal is the investigation of the effectiveness of the digital beam attenuator (DBA) in eliminating the errors in quantitation of iodine thickness resulting from radiation scatter within the patient and veiling glare in the image intensifier portion of the video image process. The loss of linearity between the video signal and iodine thickness due to effects of scatter and glare, as well as beam hardening effects, can be corrected in part by the reduction of the spatial variation of the scatter and glare components of the transmitted x-ray beam with the use of the DBA. This will make it possible to obtain accurate values for absolute iodine thickness with videodensitometry and, thus, results in absolute values for ventricle volume, ventricular ejection fraction, vessel size and flow rate which do not rely on a specific model. Specific aims include: (1) design and construction of necessary hardware for implementation of videodensitometry on the existing image processor, (2) preliminary measurement of scatter and glare with phantom materials without the DBA, (3) development of a videodensitometry algorithm with the DBA including corrections for beam hardening effects, (4) quantification of ioding thickness in DSA-produced images with the final videodensitometry system.